To satisfy a space patrol telescope system with high angular resolution, large space area and high stray light suppression, the stray light environmental characteristics at low earth orbit are summarized. In accordance with the parameters, which diameter is 1.5m, focal length is 20m, field of view is 1.1°×1°, and the optical and mechanical structure joint-design stray light suppression is compared and analyzed for on-axis cross type, off-axis back end type and off-axis sideway type. A method of optical and mechanical structure joint-design stray light suppression is proposed to reduce the stray light suppressing angle to enhance the efficiency of the observation time and sky patrol efficiency in orbit. The detailed stray light suppression design and optimization of off-axis sideway type is given. The simulation and analysis of total optical and mechanical periodic line is presented, and the major stray ray path is simulated and analyzed.Compared with the other two types, the off-axis sideway type presents the best performance of image quality and stray light suppression. The modulation transfer functions (MTF) approach the diffraction limit at all fields. When the evadable angle out of the field is 40°, the PST is less than 10<sup>-11</sup> and the system can approach to the stray light suppression limitation.
The precisely extraction of construction areas in remote sensing images can play an important role in territorial planning, land use management, urban environments and disaster reduction. In this article, we propose a method for extracting construction areas using Gaofen-1 panchromatic remote sensing images by adopting the improved Pantex<sup></sup> (a procedure for the calculation of texture-derived built-up presence index) and unsupervised classification. First of all, texture cooccurrence measures of 10 different directions and displacements are calculated. In this step, we improve the built-up presence index that we use the windows size of 21*21 to calculate the GLCM contrast measure instead of 9*9 according to the spatial resolution of Gaofen-1 panchromatic image. Then we use the intersection operator “MIN” to combine the 10 different anisotropic GLCM contrast measure to generate the final built-up presence index result. At last, we use the unsupervised classification method to classify the Pantex result into two classes and the one with larger cluster center is the construction area class. Confusion matrix of Beijing-Tianjin-Hebei region experiment shows that this method can effectively and accurately extract the construction areas in Gaofen-1 panchromatic images with the overall accuracy of more than 92%.
Satellite telemetry is the vital indicators to estimate the performance of the satellite. The telemetry data, the threshold
range and the variation tendency collected during the whole operational life of the satellite, can guide and evaluate the
subsequent design of the satellite in the future. The rotational parts on the satellite (e.g. solar arrays, antennas and
oscillating mirrors) affect collecting the solar energy and the other functions of the satellite. Visualization telemetries
(pictures, video) are captured to interpret the status of the satellite qualitatively in real time as an important supplement
for troubleshooting. The mature technology of commercial off-the-shelf (COTS) products have obvious advantages in
terms of the design of construction, electronics, interfaces and image processing. Also considering the weight, power
consumption, and cost, it can be directly used in our application or can be adopted for secondary development. In this
paper, characteristic simulations of solar arrays radiation in orbit are presented, and a suitable camera module of certain
commercial smartphone is adopted after the precise calculation and the product selection process. Considering the
advantages of the COTS devices, which can solve both the fundamental and complicated satellite problems, this
technique proposed is innovative to the project implementation in the future.
The multi-angle polarization technique, which uses the intensity of polarized radiation as the observed quantity, is a new remote sensing means for earth observation. With this method, not only can the multi-angle light intensity data be provided, but also the multi-angle information of polarized radiation can be obtained. So, the technique may solve the problems, those could not be solved with the traditional remote sensing methods. Nowadays, the multi-angle polarization technique has become one of the hot topics in the field of the international quantitative research on remote sensing. In this paper, we firstly introduce the principles of the multi-angle polarization technique, then the situations of basic research and engineering applications are particularly summarized and analysed in 1) the peeled-off method of sun glitter based on polarization, 2) the ocean color remote sensing based on polarization, 3) oil spill detection using polarization technique, 4) the ocean aerosol monitoring based on polarization. Finally, based on the previous work, we briefly present the problems and prospects of the multi-angle polarization technique used in China’s ocean color remote sensing.
In order to ensure the radiometric imaging quality for the space-borne camera with super-wide field of view, we put forward a new method, with which the apparent spectral radiance for any field of view can be precisely calculated. Firstly, building the imaging model for the space-borne camera, and the parameters of the orbits and attitudes of satellite, the look direction for the given field of view, the characteristics of different ground objects, the state of the atmosphere, et al.. Secondly, calculating the geometrical observation parameters for the given look direction of the space-borne camera. Finally, using the radiative transfer model to calculate the value of the apparent spectral radiance. Then, we use this method to calculate the apparent spectral radiance for the space-borne camera with the FOV of 75°based on freeform mirror on a small remote sensing satellite. And the result shows that the relative non-consistency of the apparent spectral radiance can be 25.3%, when the satellite takes the imaging of the area of North Atlantic. And we should greatly consider the characteristic of the radiometric imaging quality for the space-borne camera with super-wide field of view.
Based on the maximum detection range, the detection capability of space-based camera for space debris is analyzed in the paper. We perform grid generation method on the debris target and analyze the shadowing effects among the grids, building the geometry modeling of cone target sequentially. The calculation model of optical infrared characteristics is established, taking into consideration the target self-radiation and radiation reflection characteristics of the material on surface. The radiation energy of the target is only depended on the reflection of earth’s radiation and its self-radiation in the simulation proposed in the paper. Based on the maximum detection range formula, the numerical simulation presented shows that when the space-based target radiation intensity is 21.54W/sr and optical system aperture is 0.5m, the maximum detection range is 17279km. The simulation results theoretically contribute to the estimation of camera parameters and analysis on the detection capability.
The freeform optics is extensively applied in the fields of aerospace, aviation, lighting, medical treatment, et al.. For the linearly push-broom space-borne imager, integration time of different field of view can be affected by the optical system design of the imager, orbits of the satellite, maneuver of the attitudes, rotation of the Earth, light delay due to the refraction and transmission of the atmosphere, terrain error and so on. The dynamically imaging quality should be affected by the accuracy and adjusting mode of the integration time. In this paper, a new method which is especially appropriate to imaging model simulating and integration time calculating for the wide-field-of-view remote sensor is proposed. Then, the integration time of specified viewing direction for the imager with a single projection center and a super-wide field of view based on freeform mirror, which is mounted on a sun-synchronous orbit satellite, is calculated. And influence on imaging quality of adjusting integration time of different grouping modes for the focal plane assembly is analyzed. The results indicate that with the constraint condition of satellite roll angle and the modulation transfer function (MTF) influence factor no more than 20°and 2% respectively, integration time of all CCDs for the whole focal plane assembly divided into two groups with each adopting the uniform integration time, can fulfill the requirements of the imaging quality for the imager.
Proc. SPIE. 9621, 2015 International Conference on Optical Instruments and Technology: Advanced Lasers and Applications
KEYWORDS: LIDAR, Space telescopes, Telescopes, Signal to noise ratio, Atmospheric modeling, Atmospheric optics, Solid state lasers, Laser systems engineering, Pulsed laser operation, Atmospheric sensing
Many studies have indicated that the optimum measurement approach for winds from space is a pulsed coherent wind lidar, which is an active remote sensing tool with the characteristics that high spatial and temporal resolutions, real-time detection, high mobility, facilitated control and so on. Because of the significant eye safety, efficiency, size, and lifetime advantage, 2μm wavelength solid-state laser lidar systems have attracted much attention in spacebased wind lidar plans. In this paper, the theory of coherent detection is presented and a 2μm wavelength solid-state laser lidar system is introduced, then the ideal aperture is calculated from signal-to-noise(SNR) view at orbit 400km. However, considering real application, even if the lidar hardware is perfectly aligned, the directional jitter of laser beam, the attitude change of the lidar in the long round trip time of the light from the atmosphere and other factors can bring misalignment angle. So the influence of misalignment angle is considered and calculated, and the optimum telescope diameter(0.45m) is obtained as the misalignment angle is 4 μrad. By the analysis of the optimum aperture required for spacebased coherent wind lidar system, we try to present the design guidance for the telescope.